chore(dfxvm-installer): install script maintenance

[ericswanson-dfinity]

Description

• Copied the latest check_help_for() and downloader() from https://github.com/rust-lang/rustup/blob/master/rustup-init.sh (rust-lang/rustup@5bf15e3)
  • Modified to also recognize Darwin major versions 12, 13, and 14.
  • This adds retry functionality and improves tls/ciphersuite detection and use.
• Reworked the tarball extraction slightly to avoid having to rm -rf the temp directory later.
• Removed two unused functions.

Fixes https://dfinity.atlassian.net/browse/SDK-758

How Has This Been Tested?

Tested on:

• Macos Ventura, Sonoma, and Mojave (10.14) with curl
• docker run -it ubuntu with wget and curl

Checklist:

• The title of this PR complies with Conventional Commits.